How can I use 2.80 mode!s in 2.79?
2.8 was a compatibly braking release, meaning files edited in 2.8x will not work in older versions, even 2.79b.
That interface acting weird is normal and expected when opening a 2.8x file in 2.7x (or any pre 2.8 version). I've had blender flat out crash when trying to open a 2.8 file.
Fear not, you are not locked to 2.8.
Create a new file in blender 2.7x  and append whatever you need from the 2.8 file. I have had appending the whole scene fail, but appending objects always worked for me. Simply
From the Info window File &gt; Append or ShiftF1 then find the 2.8 file. Go to the objects category, and if needed simply select everything.
Proof this really works
I just tested this with this Tesla Model S made for eevee. It is setup for eevee so obviously it's 2.8, even the description says &quot;Blender 2.80 required&quot;
Yet I simply selected all the objects when appending and as you can see it works perfectly (even the materials!)